fix(campaigns): guard against null taxonomy entries in prompt descriptions

[jason10lee]

Changes proposed

Guards promptDescription() and warningForPopup() in utils.js against null/non-array taxonomy data (tags, categories, campaign_groups) that causes the Campaigns admin page to crash with TypeError: Cannot read properties of null (reading 'name').

Uses Array.isArray() + .filter(Boolean) to handle both false values from PHP's get_the_tags()/get_the_terms() and null entries from stale object cache.

How to test

1. Navigate to Audience > Campaigns — page should load normally
2. Add a mu-plugin to inject null tags:

   add_filter( 'get_the_tags', function( $terms ) {
       if ( is_array( $terms ) ) {
           $terms[] = null;
       }
       return $terms;
   } );

3. Reload Campaigns page — should still render without errors
4. Check browser console — no TypeError about null .name

Related

NPPM-2729: Campaigns admin page crashes when tag data contains null entries

[Copilot]

Pull request overview

This PR hardens the Audience → Campaigns wizard UI against malformed taxonomy data returned for prompts, preventing runtime crashes when taxonomy arrays contain false/null entries (e.g., from get_the_tags()/get_the_terms() or stale object cache).

Changes:

• Normalize campaign_groups, categories, and tags to safe arrays using Array.isArray(...) with falsy-entry removal.
• Update prompt description string-building to use the normalized taxonomy arrays.

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[jason10lee]

My only comment here as to the approach would be that maybe this fix happens too far down the tree: we own the plugin that's setting these variables, so this normalization could be happening there. Maybe the framing of the original Linear task determined the agent's choice of fix?

Still, the fix works, and could serve as part of a broader belt-and-suspenders approach with a corresponding tweak to newspack-popups.

[jason10lee]

Spotted that warningForPopup() is probably similarly affected, copied the fix over to it, and then just refactored because that's just way too many repeats. Added tests, too, because why not while we're in there?

So...the scope's creeped, but for a good cause.